JAXB注解使用小结

在JAXB中(用于JAVA对象和xml之间的转换),经常出现各类的 @XmlElement这样的标记, 下面就来以一个例子小结下,加深学习:

Jaxb处理java对象和xml之间转换常用的annotation有：

• @XmlType
• @XmlElement
• @XmlRootElement
• @XmlAttribute
• @XmlAccessorType
• @XmlAccessorOrder
• @XmlTransient
• @XmlJavaTypeAdapter

常用annotation使用说明

@XmlType

@XmlType用在class类的注解，常与@XmlRootElement，@XmlAccessorType一起使用。它有三个属性：name、propOrder、namespace，经常使用的只有前两个属性。如：

@XmlType(name = "basicStruct", propOrder = {    "intValue",    "stringArray",    "stringValue")

在使用@XmlType的propOrder 属性时，必须列出JavaBean对象中的所有属性，否则会报错。

@XmlElement

@XmlElement将java对象的属性映射为xml的节点，在使用@XmlElement时，可通过name属性改变java对象属性在xml中显示的名称。如：

@XmlElement(name="Address")　　　　private String yourAddress;

@XmlRootElement

@XmlRootElement用于类级别的注解，对应xml的跟元素，常与 @XmlType 和 @XmlAccessorType一起使用。如：

　　@XmlType　　@XmlAccessorType(XmlAccessType.FIELD)　　@XmlRootElement　　public class Address {}

@XmlAttribute

@XmlAttribute(name="Country")　　private String state;

@XmlAccessorType

　@XmlAccessorType用于指定由java对象生成xml文件时对java对象属性的访问方式。常与@XmlRootElement、@XmlType一起使用。它的属性值是XmlAccessType的4个枚举值，分　　　别为：

　　XmlAccessType.FIELD:java对象中的所有成员变量

　　XmlAccessType.PROPERTY：java对象中所有通过getter/setter方式访问的成员变量

　　XmlAccessType.PUBLIC_MEMBER：java对象中所有的public访问权限的成员变量和通过getter/setter方式访问的成员变量

　　XmlAccessType.NONE:java对象的所有属性都不映射为xml的元素

　　注意：@XmlAccessorType的默认访问级别是XmlAccessType.PUBLIC_MEMBER，因此，如果java对象中的private成员变量设置了public权限的getter/setter方法，就不要在　　　private变量上使用@XmlElement和@XmlAttribute注解，否则在由java对象生成xml时会报同一个属性在java类里存在两次的错误。同理，如果@XmlAccessorType的访问权限　　　为XmlAccessType.NONE，如果在java的成员变量上使用了@XmlElement或@XmlAttribute注解，这些成员变量依然可以映射到xml文件。

@XmlAccessorOrder

@XmlAccessorOrder用于对java对象生成的xml元素进行排序。它有两个属性值：

　　AccessorOrder.ALPHABETICAL：对生成的xml元素按字母书序排序

　　XmlAccessOrder.UNDEFINED:不排序

@XmlTransient

@XmlTransient用于标示在由java对象映射xml时，忽略此属性。即，在生成的xml文件中不出现此元素。

@XmlJavaTypeAdapter

　@XmlJavaTypeAdapter常用在转换比较复杂的对象时，如map类型或者格式化日期等。使用此注解时，需要自己写一个adapter类继承XmlAdapter抽象类，并实现里面的方法。

　　@XmlJavaTypeAdapter(value=xxx.class),value为自己定义的adapter类

　　XmlAdapter如下：

public abstract class XmlAdapter<ValueType,BoundType> {    // Do-nothing constructor for the derived classes.    protected XmlAdapter() {}    // Convert a value type to a bound type.    public abstract BoundType unmarshal(ValueType v);    // Convert a bound type to a value type.    public abstract ValueType marshal(BoundType v); }

演示例子

　1.Shop.javapackage jaxb.shop;import java.util.Set;import javax.xml.bind.annotation.XmlAccessOrder;import javax.xml.bind.annotation.XmlAccessType;import javax.xml.bind.annotation.XmlAccessorType;import javax.xml.bind.annotation.XmlAttribute;import javax.xml.bind.annotation.XmlElement;import javax.xml.bind.annotation.XmlRootElement;import javax.xml.bind.annotation.XmlType;import javax.xml.bind.annotation.XmlElementWrapper;import javax.xml.bind.annotation.XmlAccessorOrder;@XmlAccessorOrder(XmlAccessOrder.ALPHABETICAL)@XmlAccessorType(XmlAccessType.FIELD)@XmlType(name = "shop", propOrder = { "name", "number", "describer", "address","orders" })@XmlRootElement(name = "CHMart")public class Shop {    @XmlAttribute    private String name;    // @XmlElement    private String number;    @XmlElement    private String describer;    @XmlElementWrapper(name = "orders")    @XmlElement(name = "order")    private Set<Order> orders;    @XmlElement    private Address address;    public Shop() {    }    public Shop(String name, String number, String describer, Address address) {        this.name = name;        this.number = number;        this.describer = describer;        this.address = address;    }    getter/setter略//同时使用了@XmlType（propOrder={}）和@XmlAccessorOrder(XmlAccessOrder.ALPHABETICAL)，但是生成的xml只按照propOrder定义的顺序生成元素

　　2.Order.javapackage jaxb.shop;import java.math.BigDecimal;import java.util.Date;import javax.xml.bind.annotation.XmlAccessType;import javax.xml.bind.annotation.XmlAccessorType;import javax.xml.bind.annotation.XmlAttribute;import javax.xml.bind.annotation.XmlRootElement;import javax.xml.bind.annotation.XmlType;import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;@XmlType(name="order",propOrder={"shopName","orderNumber","price","amount","purDate","customer"})@XmlAccessorType(XmlAccessType.FIELD)@XmlRootElementpublic class Order {//  @XmlElement　　    private String shopName;    @XmlAttribute    private String orderNumber;//  @XmlElement    @XmlJavaTypeAdapter(value=DateAdapter.class)    private Date purDate;//  @XmlElement    private BigDecimal price;//  @XmlElement    private int amount;//  @XmlElement    private Customer customer;    public Order() {    }    public Order(String shopName, String orderNumber, Date purDate,            BigDecimal price, int amount) {        this.shopName = shopName;        this.orderNumber = orderNumber;        this.purDate = purDate;        this.price = price;        this.amount = amount;    }getter/setter略//@XmlAccessorType(XmlAccessType.FIELD)，所以此处注释掉了@XmlElement，xml中依然会生成这些元素

　　3.Customer.javapackage jaxb.shop;import java.util.Set;import javax.xml.bind.annotation.XmlType;import javax.xml.bind.annotation.XmlAttribute;import javax.xml.bind.annotation.XmlElement;import javax.xml.bind.annotation.XmlRootElement;import javax.xml.bind.annotation.XmlAccessType;import javax.xml.bind.annotation.XmlAccessorType;@XmlType@XmlAccessorType(XmlAccessType.FIELD)@XmlRootElementpublic class Customer {    @XmlAttribute    private String name;    private String gender;    private String phoneNo;    private Address address;    private Set<Order> orders;    public Customer() {    }    public Customer(String name, String gender, String phoneNo, Address address) {        this.name = name;        this.gender = gender;        this.phoneNo = phoneNo;        this.address = address;    }getter/setter略

　　4.Address.javapackage jaxb.shop;import javax.xml.bind.annotation.XmlAttribute;import javax.xml.bind.annotation.XmlType;import javax.xml.bind.annotation.XmlElement;import javax.xml.bind.annotation.XmlRootElement;import javax.xml.bind.annotation.XmlAccessType;import javax.xml.bind.annotation.XmlAccessorType;import javax.xml.bind.annotation.XmlAccessOrder;import javax.xml.bind.annotation.XmlAccessorOrder;@XmlType(propOrder={"state","province","city","street","zip"})@XmlAccessorOrder(XmlAccessOrder.ALPHABETICAL)@XmlAccessorType(XmlAccessType.NONE)@XmlRootElementpublic class Address {    @XmlAttribute　    private String state;    @XmlElement    private String province;    @XmlElement    private String city;    @XmlElement    private String street;    @XmlElement    private String zip;    public Address() {        super();    }    public Address(String state, String province, String city, String street,            String zip) {        super();        this.state = state;        this.province = province;        this.city = city;        this.street = street;        this.zip = zip;    }getter/setter略//注意：虽然@XmlAccessorType为XmlAccessType.NONE,但是在java类的私有属性上加了@XmlAttribute和@XmlElement注解后，这些私有成员会映射生成xml的元素

　　5.DateAdapter.javapackage jaxb.shop;import java.util.Date;import java.text.SimpleDateFormat;import javax.xml.bind.annotation.adapters.XmlAdapter;public class DateAdapter extends XmlAdapter<String, Date> {    private String pattern = "yyyy-MM-dd HH:mm:ss";    SimpleDateFormat fmt = new SimpleDateFormat(pattern);    @Override    public Date unmarshal(String dateStr) throws Exception {        return fmt.parse(dateStr);    }    @Override    public String marshal(Date date) throws Exception {        return fmt.format(date);    }}//用于格式化日期在xml中的显示格式，并且由xml unmarshal为java对象时，将字符串解析为Date对象

　　6.ShopTest.javapackage jaxb.shop;import java.io.FileReader;import java.io.FileWriter;import java.io.IOException;import java.math.BigDecimal;import java.util.Date;import java.util.HashSet;import java.util.Set;import javax.xml.bind.JAXBContext;import javax.xml.bind.JAXBException;import javax.xml.bind.Marshaller;import javax.xml.bind.Unmarshaller;public class ShopTest {    public static void main(String[] args) throws JAXBException, IOException{        Set<Order> orders = new HashSet<Order>();        Address address1 = new Address("China", "ShangHai", "ShangHai", "Huang", "200000");        Customer customer1 = new Customer("Jim", "male", "13699990000", address1);        Order order1 = new Order("Mart", "LH59900", new Date(), new BigDecimal(60), 1);        order1.setCustomer(customer1);        Address address2 = new Address("China", "JiangSu", "NanJing", "ZhongYangLu", "210000");        Customer customer2 = new Customer("David", "male", "13699991000", address2);        Order order2 = new Order("Mart", "LH59800", new Date(), new BigDecimal(80), 1);        order2.setCustomer(customer2);        orders.add(order1);        orders.add(order2);        Address address3 = new Address("China", "ZheJiang", "HangZhou", "XiHuRoad", "310000");        Shop shop = new Shop("CHMart", "100000", "EveryThing",address3);        shop.setOrder(orders);        FileWriter writer = null;        JAXBContext context = JAXBContext.newInstance(Shop.class);        try {            Marshaller marshal = context.createMarshaller();            marshal.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);            marshal.marshal(shop, System.out);            writer = new FileWriter("shop.xml");            marshal.marshal(shop, writer);        } catch (Exception e) {            e.printStackTrace();        }        Unmarshaller unmarshal = context.createUnmarshaller();        FileReader reader = new FileReader("shop.xml") ;        Shop shop1 = (Shop)unmarshal.unmarshal(reader);        Set<Order> orders1 = shop1.getOrder();        for(Order order : orders1){            System.out.println("***************************");            System.out.println(order.getOrderNumber());            System.out.println(order.getCustomer().getName());            System.out.println("***************************");        }    }}

　　7.生成的xml文件<?xml version="1.0" encoding="UTF-8" standalone="yes"?><CHMart name="CHMart">    <number>100000</number>    <describer>EveryThing</describer>    <address state="China">        <province>ZheJiang</province>        <city>HangZhou</city>        <street>XiHuRoad</street>        <zip>310000</zip>    </address>    <orders>        <order orderNumber="LH59800">            <shopName>Mart</shopName>            <price>80</price>            <amount>1</amount>            <purDate>2012-03-25 12:57:23</purDate>            <customer name="David">                <gender>male</gender>                <phoneNo>13699991000</phoneNo>                <address state="China">                    <province>JiangSu</province>                    <city>NanJing</city>                    <street>ZhongYangLu</street>                    <zip>210000</zip>                </address>            </customer>        </order>        <order orderNumber="LH59900">            <shopName>Mart</shopName>            <price>60</price>            <amount>1</amount>            <purDate>2012-03-25 12:57:23</purDate>            <customer name="Jim">                <gender>male</gender>                <phoneNo>13699990000</phoneNo>                <address state="China">                    <province>ShangHai</province>                    <city>ShangHai</city>                    <street>Huang</street>                    <zip>200000</zip>                </address>            </customer>        </order>    </orders></CHMart>